Need Help! Getting Invalid Shares

Hello. I have been mining for the past day or so and I cannot seem to clear the error message: invalid shares.

Some details about my system:

-AMD FX-8370E CPU @ 4.3 GHz
-Asus M5A99X EVO R.20 Mobo
-8 GB RAM
-Two GPUs: Asus Strix R9 390 8 GB, XFX R9 390 8 GB. Neither GPU is overclocked
-Windows 7 64bit with all updates installed
-Running only one miner using both GPUs
-Max MH/s benchmark rate: 53

Troubleshooting done:
-Restarted miner - no changes
-Rebooted PC - no changes
-Deleted all DAG files except the two most recent ones - no changes
-Uninstalled GPU drivers and re-install drivers again - no changes
-Confirmed mining rate is set to 51 MH/s

Please help!